The present invention relates to power capacitors having a plurality of capacitive section windings within an enclosure with fusible elements between the section windings and the external terminals of the enclosure.
Reference is made to copending application Ser. No. 298,788, filed Aug. 18, 1981 by Thiel et al. and assigned to the present assignee which discloses power capacitors of a type with which the improvement of the present invention may be used.
Internal fusing in power capacitors is a known practice to retain usefulness of the capacitor unit even if some of the individual section windings in the capacitor fail. The sections of a power capacitor normally are interconnected in series and parallel groups of individual section windings. It is desirable that if one section of a parallel group shorts out, the entire parallel group is not thereby shorted. Having a fusible connection for each of the section windings permits one to fail and to be effectively removed from the cirucit so that the remaining ones of the parallel group can perform their intended function.
Capacitors with internal fusing normally contain many more windings, typically about 25 to about 50, as compared to units having only external fusing which typically contain about 12 to about 20 sections. Therefore the internally fused units require a substantial number of fusible elements, one for each winding, which are of relatively light flexible wire, of silver or copper or alloys thereof, of a chosen length such as up to about five inches, that is sufficient for them to provide their protective function.
The delicacy of the fuse wires and their large numbers require that there be a stable mounting arrangement for them with adequate separation between them so as to avoid interaction during clearing. In addition to avoiding direct contact between adjacent fuse wires, care should be taken so that when a fuse operates by clearing, that it does not result in any rupture of neighboring fuse wires.
The present invention provides a way to mount numerous fuse wires in a capacitor unit in a manner that is both inexpensive and simple to implement while providing assurance of maintaining adequate spacing between the fuse wires. At the upper end of the stacked sections in the enclosure there is provided a means for insulatively supporting a common electrical bus that conducts from a number of paralleled sections to an external terminal. This insulative supporting means is provided by a plurality of insulative spacer elements disposed between certain adjacent ones of the sections and having an extended portion beyond the ends of the sections. The spacer elements support near their upper extremity, such as in an aperture therein, the common electrical bus that extends over the sections. The fuse wires are individually attached to their respective section windings, such as by soldering to the conductive material disposed on the ends of the windings in an extended foil capacitor, and extend to the common bus arouond an insulative locater member which may be a board-like element extending over the sections through slots in the insulative spacers that support the bus. In extending around the locator element, the fuse wires are held in a secure location against the edge of the locater. The support and location provided by the insulative board, to which the wires need not be fastened, provides adequate spacing of the fuse wires between each other. Consequently, the expense and difficulty of prior schemes for internal fusing are substantially avoided and the present invention provides a mounting and interconnection arrangement that can be readily used with various types of power capacitors including those of the extended foil type.